Embodiments of the invention relate to a pattern mask for forming a microlens, an image sensor, and a fabricating method thereof.
An image sensor is a semiconductor device that converts an optical image into an electrical signal. Representative image sensors in the related art include charge coupled devices and CMOS image sensors.
The image sensor may be fabricated by the following process.
First, transistors and photodiodes electrically connected to the transistors are formed on a semiconductor substrate, and an insulating layer structure and a wiring layer are formed on the transistors and photodiodes. Then, red, green, and blue color filters are formed on the insulating layer structure, and a positive type of photoresist film is coated on the upper surface of the color filter to form a planarization layer. Thereafter, the photoresist film is coated on the upper surface of the planarization layer and the photoresist film is patterned by an exposure process and a developing process to form a microlens.
FIG. 1 is a plan view showing a pattern mask for patterning a photoresist film in order to form a microlens in the related art.
Referring to FIG. 1, the pattern mask 1 in the related art comprises a mask body 2 and an aperture 3. In the embodiment, the aperture 3 is formed at a position where a microlens will be formed.
FIG. 2 is a plan view showing a microlens patterned using the pattern mask of FIG. 1.
Referring to FIG. 2, when forming microlenses 4 by exposing and developing a photoresist film using a pattern mask 1 of FIG. 1, the corner portions of the microlenses 4 are rounded due to various causes. When the corner portions of the microlenses 4 are rounded, the space between the corner portions of the four microlenses 4 has a large gap 5 if the microlenses 4 are arranged in a matrix form, wherein any light passing through the gap 5 that is incident on a photodiode may considerably reduce image quality.
Also, a gap 6 is generally formed between two neighboring microlenses 4 in the example of FIG. 2. At this time, the width of the gap 4 formed between the microlenses 4 may be about 100 nm to about 200 nm, wherein light incident through the gap 4 may also reduce image quality.